Digital typesetters image typographical or typeface characters coded in digital form and stored on a digital storage medium such as a magnetic tape drum or rigid or floppy disc. Such digital typesetters are normally provided with a cathode ray tube (CRT) or laser beam imaging system for writing the characters onto a light sensitive film or paper.
Such a device is shown in copending U.S. Pat. No. 4,231,096, and assigned to the common assignee. As shown in that application, a digital typesetter has an imaging system producing a one dimensional raster line across the width of the print media. This raster line is repeated down the length of the print medium to form a raster scanning system.
A digitized master font contains digitally encoded normalized characters which may be expanded or reduced in size through digital techniques, before the data is transmitted to an imaging system to form characters.
The system described in the copending application receives first digital data defining the identity, form, size and placement of the characters to be typeset. The first data is set into the system in a sequence by the typesetting composer.
The system then receives second digital data defining the contour of each character to be typeset with respect to the normalized encoded set of data.
The system then produces third digital data defining the locations of the characters boundaries intersecting each of a series of raster scan lines.
The characters are formed by modulating a light beam at the character boundary raster intersections and each of the characters are formed over a succession of raster lines.
A plurality of characters may intersect a single raster line, extending across the width of a print medium. The system then identifies the intersections of each single raster line with the boundaries of these characters. It modulates the beam at the intersection points to image that portion of the character intersecting that single raster line. It then continues the process for the succession of raster lines.
A character imaging device such as a laser scanner is connected to a line storage buffer which stores the location data for the character intersections. This data is then provided to the imaging device to image the character on the succession of raster lines and on a print medium.
The first digital data defining the identity, form, size and placement of the characters to be typeset originates from a word processing system.
As is typical and well-known in such systems, an operator may sit at a keyboard, and by known techniques insert a text which is then stored on a storage medium, such as a floppy disc, and justified. The sequence of the text stored in data form usually is identical to the sequential input of the data by the composer.
As described in the cross-referenced applications, the second digital data for the fonts comprises a series of digital numbers defining the coordinates of the start points of character outlines and the length and direction of a plurality of straight line vectors extending successively along the character outlines from these start points. The second digital data is encoded on a normalized coordinate system. The length and direction of each vector is represented by first and second coordinate distances.
The data processing system additionally employs a memory for storing fourth digital data derived from the first and second digital data and used to generate the said third digital data.
The fourth digital data defining the character is arranged within an internal memory in sequentially addressable locations. The fourth digital data is then given to the output data system for conversion into character boundary information according to its sequential arrangement.
In composing text, the composer follows the typical convention of writing from left to right and from the top of the page to the bottom of the page.
Without other added steps, the data is then physically located in the storage medium in the same sequence as it was placed into the system. It follows this input sequence starting with the left upper corner of a text page, proceeding across the page in the width direction and then when a line is completed, proceeds down a line in the ascending order of the lines. The sequence then continues across the page width, and down another line increment in the same ascending order.
Ascending order as used here and in the description of the invention is a convention chosen to explain the invention and assumes the line value at the top of a page of text starts with 1 and the lines increase in value as lines are generated from the top to the bottom of the text page. However, as will be seen, the principles of the invention are the same regardless of the convention chosen.
When the data is to be imaged on a raster screen, and across a series of successive raster lines generated in ascending order along one dimension of the print medium, the data may be read out in the same sequence it is written into memory or in a FIFO sequence.
In this case, data to the left most position on the page for a line would be read out first and each successive character across the width dimension of the page can then be accessed to provide information to modulate the beam.
However, in composing characters, especially in typesetting, a succession of characters may be put on a line, with successive characters towards the right hand side of the page, in larger character size than those characters on the same line and towards the left side of the page. Additionally, characters of the same size may be placed on a higher base line relative to those characters closer to the left side of the page. Where these characters have raster lines in common, those characters placed towards the right side of the page will be located on raster lines having a lower ascending order then characters placed towards the left side of the page. Where the character data is accessed, in the same sequence it was put into the system, those characters towards the right side of the page and imaged across raster lines with a lower ascending order would be imaged out of sequence with the order of the raster lines and the upper portion of these characters would not be imaged.
Where the character data is placed into the store in the exact text setting sequence, for example from left to right, then following that sequence, data for the left most characters would be provided first to the output system. This data would not be accessed until the raster line sequence had progressed in ascending order to a value corresponding to and beginning with the most left side character data. Where the data is retrieved from the system in the input sequence, the data for the characters on the right side of the page, having portions extending above the left side characters but intersecting common raster lines would be accessed later in time. That data would be provided to the output system on a real time basis after the raster lines corresponding to that data had been imaged.
On a real time basis, those characters to the right of the page would be accessed after the raster line sequence had proceeded past the point where portions of those characters were to be imaged. Those portions of those characters would be lost.
Where characters are all of the same size and located on a common base line, the size and placement of the characters may take any form.
However, in a system where the character contours are stored in a digital data base, and where that data base is used to compute character intersection points, the data representing those characters must be accessed and provided to the output system, in the sequence of raster lines. If the situation were otherwise, portions of characters would be lost as explained above, and the capability of such a system to display characters of random sizes and at random locations from a normalized encoded font would be lost.